1. Field of the Invention
The present invention relates to a method of grinding a curved corner portion of a workpiece by a grinding wheel whose edge has a curvature radius smaller than that of the curved corner portion.
2. Description of the Prior Art
In a conventional method of grinding a curved corner portion, whose curvature radius is larger than that of an edge portion of a grinding wheel, the grinding wheel is first moved inwardly through a predetermined distance to grind the curved corner portion at the time when the grinding wheel G is located at the end portion of the curved corner portion. Next, the grinding wheel is moved along the profile of the curved corner portion at a predetermined feed rate by controlling the relative movement of the grinding wheel and the workpiece so as to grind the curved corner portion. In this method, however, the grinding efficiency is low because only abrasive grains which are disposed at the side of the advance are effective to grind the workpiece. Therefore, the infeed amount of the grinding wheel per each traverse feed movement of the workpiece must be small, and the traverse feed rate cannot be high.
To overcome this drawback, it has been proposed to grind the curved corner portion with a plunge grinding operation just as grinding a cylindrical portion of the workpiece. In this method, the grinding wheel is first retracted from an advanced position to a predetermined retracted position, and then the table is moved so as to relatively position the workpiece at a grinding start position. Subsequently, the grinding wheel is moved inwardly from the grinding start position to the advanced position to perform a plunge grinding operation for grinding a portion of the curved corner portion. In this method, since each retracted position or grinding start position is included in a line extending parallel to the axis of rotation of the workpiece, the movement amount of the grinding wheel from the grinding start position to the advanced position is changed depending on the movement of the grinding wheel along the axis of the workpiece. This results in the increase of air-cut grinding feed amount which is not effective in actual grinding. Therefore, the grinding cycle time cannot be shortened.